1. Field of the Invention
The present invention relates to a printing unit used for a perfecting multi-color printing press and a sheet-fed perfecting multi-color printing press containing such a printing unit, and manufacturing methods therefor.
More particularly, it relates to a printing unit used for a printing press, in which multi-color offset printing can be performed on both top and back surfaces of a sheet by one passing operation of sheet, and a sheet-fed perfecting multi-color printing press containing such a printing unit, and manufacturing methods therefor.
2. Description of the Related Art
Conventionally, as a sheet-fed perfecting multi-color printing press using a lithographic press technology represented by an offset printing press, what is called a press of a reversing type perfecting printing system, what is called a press of a B—B type perfecting printing system, and others are known.
As the above-mentioned reversing type perfecting printing system, there is available a press made up of a back surface printing section, a top surface printing section, a sheet reversing section, etc., in which after multi-color printing is performed on the back surface of a sheet by the back surface printing section, the sheet is reversed by the sheet reversing section and the reversed sheet is transferred to the top surface printing section, by which multi-color printing is performed on the top surface of the sheet by the top surface printing section (for example, Japanese Patent Publication No. 1-56672 (No. 56672/2001).
As the above-mentioned B—B type perfecting printing system, a printing unit is configured in which a plurality of blanket cylinders and impression cylinders with a rubber blanket affixed thereon are provided alternately in parallel with each other in the horizontal direction, a plate cylinder, ink mechanism, dampening water mechanism, etc., are provided above each of the blanket cylinders and below each of the impression cylinders. This printing unit is configured so that a gripper is provided on each of the blanket cylinders and impression cylinders, and during the time when a sheet is conveyed, multi-color printing is performed on both surfaces of the sheet at the same time has been disclosed in Japanese Patent Provisional Publication No. 58-147364 (No. 147364/1983).
In the reversing type perfecting printing system, the printing speed is lower than that of a one-side printing press, and the register accuracy of printing is liable to be degraded. Also, when the sheet size is changed, much labor and time is required for the change and adjustment of position of gripping using a gripper at the rear end of sheet, and a usable sheet size is limited. Further, a reversing mechanism requires two sheet transfer cylinders and a reversing cylinder, which presents a problem of increased total length of printing press.
Also, in the B—B type perfecting printing system, a delicate difference arises between the cylinder finish dimensions of the two blanket cylinders as a result of an error of blanket thickness, and thus mackle etc. sometimes occur. Also, in the B—B type perfecting printing system, there is no impression cylinder that serves as the reference plane at the time when a printing pressure is applied, which presents a problem of no sharpness of printed matter.
Therefore, as a technically preferred printing system, a press of a two-stage type represented by an same-floor type and a press of an impression cylinder connecting type are available.
As a press of the two-stage type represented by the same-floor type, Japanese Patent Provisional Publication No. 7-9654 (No. 9654/1995) has disclosed a sheet-fed perfecting multi-color printing press in which a top surface printing section, in which a blanket cylinder, a plate cylinder, and an inking mechanism are provided above an impression cylinder provided with a sheet gripper to form a top surface printing unit and a plurality of the top surface printing units are arranged in parallel, and a back surface printing section, in which a blanket cylinder, a plate cylinder, and an inking mechanism are provided below an impression cylinder provided with a sheet gripper to form a back surface printing unit and a plurality of the back surface printing units are arranged in parallel, are connected by impression cylinders so that a line connecting the axes of impression cylinders constituting the printing sections is substantially horizontal. Also, the Publication has disclosed a sheet-fed perfecting multi-color printing press in which a top surface printing section, in which a blanket cylinder, a plate cylinder, and an inking mechanism are provided above an impression cylinder provided with a sheet gripper to form a top surface printing unit and a plurality of the top surface printing units are arranged in parallel, and a back surface printing section, in which a blanket cylinder, a plate cylinder, and an inking mechanism are provided below an impression cylinder provided with a sheet gripper to form a back surface printing unit and a plurality of the back surface printing units are arranged in parallel, are connected by an even number of sheet transfer cylinders.
Specifically, a perfecting printing operation is performed by the two-stage type in which a plurality of top surface printing units are arranged in parallel to perform printing on top surface and then a plurality of back surface printing units are arranged in parallel to perform printing on back surface.
In this case, especially in the latter press, the height of an equipment portion for printing on the opposite surface after printing on one surface has been finished can be adjusted. Therefore, by using what is called an same-floor type as shown in FIG. 1, the construction of the whole printing press can be made compact.
As a press of an impression cylinder connecting type, Japanese Patent Provisional Publication No. 6-336003 (No. 336003/1994) discloses a sheet-fed perfecting printing press. This printing press is constructed so that a blanket cylinder, a plate cylinder, and an inking mechanism are provided above an impression cylinder provided with a sheet gripper to form a top surface printing unit, and a blanket cylinder, a plate cylinder, and an inking mechanism are provided below an impression cylinder provided with a sheet gripper to form a back surface printing unit. The top surface printing unit and the back surface printing unit are connected to each other by the impression cylinders constituting the printing units.
Comparing the two-stage type and the impression cylinder connecting type, in the former type, the printing on the back surface is started after the printing on the top surface has been finished, so that there is less fear of stained prints. Also, in the former type, when the number of colors used on the top and back surfaces is different, there is less need for providing useless equipment. On the other hand, it is less compact than the latter type.
On the other hand, although the latter type is superior to the former type in compactness, it is unsuitable to the printing on thick sheets, and in the latter type, there is a fear of stained prints because printing operations on the top and back surfaces are performed alternately. Also, the latter type has a drawback in that the same number of printing units are required even when the number of colors used on the top and back surfaces is different.
For these reasons, at present, the above-mentioned two types are practically used according to the purposes for which they are used.